Researchers observed 447 psychology students at the University of East London who were in foundation, first and second year.

They found the students who performed better in the exams tended to be those who took water into the exam - with an average improvement of 4.8% - potentially enough to move a student into a higher grade boundary.

The research paper said information about the importance of staying hydrated during exams should be targeted at younger students in particular.

Dr Chris Pawson, from the University of East London, said consuming water may have a physiological effect on thinking functions that lead to improved exam performance.

Water consumption may also alleviate anxiety, which is known to have a negative effect on exam performance, explained Dr Pawson.

“Future research is needed to tease apart these explanations, but whatever the explanation it is clear that students should endeavour to stay hydrated with water during exams,” he said.

Dr Mark Gardner, from the University of Westminster, explained: “Supplementing with water is a really cheap way students and educators can help get better results.”